keyboard circuit? (& MB standard??)

[Arch-lab]

Hi,
I have seen schematics that don't put pullups on the clock and data lines for
a ps/2 keyboard. Others do... Is it a standard that PC motherboards provide the
pullups??
I.e. I would like to avoid being redundant if possible. Do most "real"
keyboards have pullups? Or are they on the motherboard?


Thanks for any help

 

[petrus bitbyter]

"Arch-lab" <lab@us.com> schreef in bericht newsSmbc.99$mn3.79@clgrps13...

Hi,
I have seen schematics that don't put pullups on the clock and data
lines for
a ps/2 keyboard. Others do... Is it a standard that PC motherboards
provide the
pullups??
I.e. I would like to avoid being redundant if possible. Do most "real"
keyboards have pullups? Or are they on the motherboard?


Thanks for any help

As these lines are bidirectional they need pullups. But there's no need for
you to see them. They may be inside the chip for instance.

petrus


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[Arch-lab]

Yes, I know this (actually it isn't because they are "bidirectional", but
because they are OC).

My point is though was, is it the PS/2 spec.for which side has to have them?
e.g. does a PC keyboard have pullups, or does the motherboard side of a PS/2
bus have pullups. Or is it spec'ed that both should (redunantly) have it?

As these lines are bidirectional they need pullups. But there's no need for
you to see them. They may be inside the chip for instance.

petrus


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[Roland]

Hi

I'm pretty sure they are in the computer because if they were not then the
lines would float low with no KB and the computer will assume the slave it
holding them low and never send anything.

I have never seen a spec to say either way, but I have never seen a ps2 line
at 0V in idle. I don't use pull ups with a keyboard emulator I make and
haven't run into problems yet. Check the specs on some PS/2 interface chips.

Rol


"Arch-lab" <lab@us.com> wrote in message newsSmbc.99$mn3.79@clgrps13...

Hi,
I have seen schematics that don't put pullups on the clock and data
lines for
a ps/2 keyboard. Others do... Is it a standard that PC motherboards
provide the
pullups??
I.e. I would like to avoid being redundant if possible. Do most "real"
keyboards have pullups? Or are they on the motherboard?


Thanks for any help

 

[Arch-lab]

It is actually because they are OC, not because they are bidirectional.

However, I would like to find out if this is a STANDARD.

I.e. Can I count on a Motherboard having PS/2 pullups, or should my keyboard
also have them??

As these lines are bidirectional they need pullups. But there's no need for
you to see them. They may be inside the chip for instance.

petrus


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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.639 / Virus Database: 408 - Release Date: 23-3-2004